A novel structural damage identification approach using damage-induced perturbation in longitudinal vibration

Abstract

Structural damage identification approaches relying on structural vibration shapes (VSs) have been widely developed. Among the approaches, the pseudo-force approach has attracted increasing attention during the recent decade owing to the fact that the damage-induced pseudo-force is concentrated within the damage region only and rapidly attenuates at undamaged locations. Transverse pseudo-forces (TPFs) relying on flexural VSs have been used for structural damage identification. However, the TPF approach is inapplicable to some structures governed mainly by tension and not bending, such as cables in a cable-stayed bridge, because bending effects on their flexural vibrations are much smaller compared to their tension effects. In contrast, longitudinal VSs can be useful for identifying such damages, although they are much more difficult to measure than flexural VSs. In this study, a new concept of axial pseudo-force (APF) is formulated using damage-induced perturbation in longitudinal vibration, which forms the basis of a novel damage identification approach for longitudinally vibrating structures. Unlike the TPF approach relying on transverse bending, the proposed APF approach relies on axial tension/compression. In particular, a damage index (DI) is established to indicate and locate structural damage. The multiscale analysis is integrated into the DI to enhance its robustness against environmental noise interference. A normalization strategy is further proposed to deal with unknown material and structural parameters in practical scenarios. The capability of the approach in identifying damage in longitudinally vibrating structures is analytically verified on bars with two-sided notches. The applicability of the approach is experimentally validated by identifying a two-sided notch in an aluminum bar whose longitudinal VSs were acquired through non-contact vibration measurement using a three-dimensional (3D) scanning laser vibrometer (SLV).